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681.
682.
A new numerical technique for simulating the coupled seismic and electromagnetic waves in layered porous media
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Chen's technique of computing synthetic seismograms,which decomposes every vector with a set of basis of orthogonality and completeness before applying the Luco-Apsel-Chen(LAC)generalized reflection and transmission coefficients method,is confirmed to be efficient in dealing with elastic waves in multi-layered media and accurate in any frequency range.In this article,we extend Chen's technique to the computation of coupled seismic and electromagnetic(EM)waves in layered porous media.Expanding the involved mechanical and electromagnetic fields by a set of scalar and vector wave-function basis,we obtain the fundamental equations which are subsequently solved by using a recently developed version of the LAC generalized reflection and transmission coefficients method.Our approach and corresponding program is validated by reciprocity tests.We also show a numerical example of a two-layer model with an explosion source.The P-to-EM conversion waves radiated from the interface may have potential application. 相似文献
683.
L. E. Sjöberg 《Journal of Geodesy》2003,77(3-4):139-147
Assuming that the gravity anomaly and disturbing potential are given on a reference ellipsoid, the result of Sjöberg (1988, Bull Geod 62:93–101) is applied to derive the potential coefficients on the bounding sphere of the ellipsoid to order e
2 (i.e. the square of the eccentricity of the ellipsoid). By adding the potential coefficients and continuing the potential downward to the reference ellipsoid, the spherical Stokes formula and its ellipsoidal correction are obtained. The correction is presented in terms of an integral over the unit sphere with the spherical approximation of geoidal height as the argument and only three well-known kernel functions, namely those of Stokes, Vening-Meinesz and the inverse Stokes, lending the correction to practical computations. Finally, the ellipsoidal correction is presented also in terms of spherical harmonic functions. The frequently applied and sometimes questioned approximation of the constant m, a convenient abbreviation in normal gravity field representations, by e
2/2, as introduced by Moritz, is also discussed. It is concluded that this approximation does not significantly affect the ellipsoidal corrections to potential coefficients and Stokes formula. However, whether this standard approach to correct the gravity anomaly agrees with the pure ellipsoidal solution to Stokes formula is still an open question. 相似文献
684.
~~THE CCA BETWEEN 500 hPa GEOPOTENTIAL HEIGHT FIELDS OVER NORTHERN HEMISPHERE AND RAINFALL OF CHINA IN MAY@严华生$Department of Earth Sciences, Yunnan University, Kunming 650091 China
@陈艳$Yunnan Meteorological Science Institute, Kunming 650034 China
@郭世昌$Department of Earth Sciences, Yunnan University, Kunming 650091 China
@王会军$Institute of Atmospheric Physics, Academy of Sciences, Beijing 100091 China~~ Project "973" (G1998040905)… 相似文献
685.
Freeden Willi Groten Erwin Michel Volker Arfa-Kaboodvand Kourosh 《Studia Geophysica et Geodaetica》2003,47(1):37-72
Harmonic wavelets are introduced within the framework of the Sobolev-like Hilbert space H of potentials with square-integrable restrictions to the Earth's (mean) sphere
R
. Basic tool is the construction of H-product kernels in terms of an (outer harmonics) orthonormal basis in H. Scaling function and wavelet are defined by means of so-called H-product kernels. Harmonic wavelets are shown to be building blocks that decorrelate geopotential data. A pyramid scheme enables fast computations. Multiscale signal-to-noise thresholding provides suitable denoising. Multiscale modelling of the Earth's anomalous potential from EGM96-model data is illustrated by use of bandlimited harmonic wavelets, i.e. Shannon and CP-wavelets. 相似文献
686.
Gas-surface interactions and satellite drag coefficients 总被引:1,自引:0,他引:1
Information on gas-surface interactions in orbit has accumulated during the past 35 years. The important role played by atomic oxygen adsorbed on satellite surfaces has been revealed by the analysis of data from orbiting mass spectrometers and pressure gauges. Data from satellites of special design have yielded information on the energy accommodation and angular distributions of molecules reemitted from satellite surfaces. Consequently, it is now possible to calculate satellite drag coefficients from basic physical principles, utilizing parameters of gas-surface interactions measured in orbit. The results of such calculations are given. They show the drag coefficients of four satellites of different compact shapes in low-earth orbit with perigee altitudes in the range from about 150 to 300 km, where energy accommodation coefficients and diffuse angular distributions have been measured. The calculations are based on Sentman's analysis of drag forces in free-molecular flow. His model incorporates the random thermal motion of the incident molecules, and assumes that all molecules are diffusely reemitted The uncertainty caused by the assumption of diffuse reemission is estimated by using Schamberg's model of gas-surface interaction, which can take into account a quasi-specular component of the reemission. Such a quasi-specular component is likely to become more important at higher altitudes as the amount of adsorbed atomic oxygen decreases. A method of deducing accommodation coefficients and angular distributions at higher altitudes by comparing the simultaneous orbital decay of satellites of different shapes at a number of altitudes is suggested. The purpose is to improve thermospheric measurements and models, which are significantly affected by the choice of drag coefficients. 相似文献
687.
Richard L. Branham Jr. 《Celestial Mechanics and Dynamical Astronomy》1990,49(2):209-217
Hansen coefficients are used in expansions of the elliptic motion. Three methods for calculating the coefficients are studied: Tisserand's method, the Von Zeipel-Andoyer (VZA) method with explicit representation of the polynomials required to compute the Hansen coefficients, and the VZA method with the values of the polynomials calculated recursively. The VZA method with explicit polynomials is by far the most rapid, but the tabulation of the polynomials only extends to 12th order in powers of the eccentricity, and unless one has access to the polynomials in machine-readable form their entry is laborious and error-prone. The recursive calculation of the VZA polynomials, needed to compute the Hansen coefficients, while slower, is faster than the calculation of the Hansen coefficients by Tisserand's method, up to 10th order in the eccentricity and is still relatively efficient for higher orders. The main advantages of the recursive calculation are the simplicity of the program and one's being able to extend the expansions to any order of the eccentricity with ease. Because FORTRAN does not implement recursive procedures, this paper used C for all of the calculations. The most important conclusion is recursion's genuine usefulness in scientific computing. 相似文献
688.
689.
D. Tsoulis 《Journal of Geodesy》2004,78(1-2):7-11
The spherical harmonic analysis of the 2×2 density and stratification information contained in the global crustal model CRUST 2.0 is presented from the viewpoint of gravity field recovery and interpretation. Using a standard Airy/Heiskanen (A/H) isostatic hypothesis and a radially distributed compensation mechanism, two models of topographic/isostatic (t/i) potential harmonic coefficients are obtained up to degree and order 90. The CRUST-derived coefficients are compared with the spectrum of uncompensated topography, with the EGM96 observed gravity field, and with the t/i spectrum based on an A/H hypothesis with a constant compensation depth of 30 km. The signal degree variances of both CRUST models decrease quite smoothly towards degree 90, while the seven-layer model approaches the EGM96 spectrum for degrees 80–90. The significant deviation of the CRUST spectra from the A/H combined spectrum may prove of relevance to local and regional applications investigating the validity of current isostatic hypotheses.Acknowledgments. Sincere thanks go to Nikolaos Pavlis and three unknown referees for their thoughtful comments. Figure 1 has been produced using the mapping package m_map by R. Pawlowicz, which is a MATLAB toolbox that can be freely downloaded from http://www2.ocgy.ubc.ca/~rich/map.html 相似文献
690.
Information theory makes it possible to judge and evaluate methods and results in chemical analysis. Theobtained information can be expressed in different ways. One way is to define information as the decreaseof uncertainty after analysis. Conditional probabilities are therefore considered when evaluating theinformation provided by qualitative analyses. However, the use of other information measures, such asthe information gain, is often preferable. In multicomponent analysis the translation of information fromsignals to the amounts of the analytes has been investigated along with the relevance of individualcomponents. Information theory can also be applied to find the optimum experimental conditions. Theevaluation of the properties of analytical methods by information theory has been proposed. 相似文献